Flip-chip devices are typically composed of a semiconductor device, or die, mounted on a substrate. Near the top of the semiconductor die, circuits are formed in an active area. The remaining part of the semiconductor die is an inactive area. In order to make electrical connection between the circuit on the semiconductor die and the substrate, the semiconductor die is flipped. Thus, the active area is in proximity to the substrate. This is in contrast to conventional semiconductor devices, which mount the inactive portion of the semiconductor die to a substrate.
After fabrication of the flip-chip device, it is often desirable to detect features, such as faults, within the semiconductor die or investigate other features within the circuit. In order to do so, the inactive area is thinned from the back side of the die. Thus, a surface within the inactive area is exposed. This surface will also be referred to as the back side. An infrared microscope or other mechanism may be used to image faults in the semiconductor die. Once the location of the fault is determined, the semiconductor die around the fault may be deprocessed in order to determine the exact nature of the fault.
Deprocessing the semiconductor die typically includes milling away a portion of inactive area. In order to mill a portion of the semiconductor die, the die is typically removed from the infrared microscope and placed in a mill. Typically, the diameter of the ion beam used to mill a portion of the semiconductor is much larger than the size of the fault detected and much smaller than the die itself. Thus, the desired milling location is determined.
Typically, the desired milling location is determined based on an attribute on the back side of the semiconductor die. The conventional method for deprocessing commences by choosing a particular attribute on the back side of the semiconductor die. Alternatively, the conventoinal method may commence by creating an attribute at the edge of the back side of the die, for example using a laser. When imaging the fault in the infrared microscope, a user determines the location of the fault with respect to the attribute. When the semiconductor die is moved to the mill, the user utilizes the knowledge of the location of the fault with respect to the attribute to navigate from the attribute to the fault. The user then mills in the area of the fault.
Although the conventional method allows a user to deprocess a portion of the semiconductor die, the conventional method is time consuming and subject to error. The size of the attribute on the back side of the die is typically large in comparison to the fault size. When navigating from the attribute to the fault in the mill, errors may be made. The center of the portion of the semiconductor die being milled may be away from the location of the fault. As a result, when the portion is milled, the fault may not be exposed. The user then must perform milling in a new location believed to be closer to the fault. This milling is extremely time consuming and tedious. In addition, the process of navigating from the attribute to the fault is also time consuming. Thus, deprocessing is made more difficult.
Accordingly, what is needed is a system and method for more accurately marking the location of the fault in a semiconductor die. The present invention addresses such a need.